Television picture tube screen



July 14, 1942. L. MALTER TELEVISION PIVCTURE TUBE SCREEN Filed Nov. 50,1940 Fifa. 1.

DIRECT] 0N OF' .BE/7M JJ/RL'C "flo/v :Smoentor L0 ,LL L6 Mal t e r 0F'BE/7M f (Ittorneg particularly to Patented July 14, 1942 TELEVISIONPICTURE TUBE SCREEN Louis Malter, Newark, N. I., assignor to Radio`Corporation of America, a corporation of Dela- Ware application Novemberso, 1940, seriaiNo. 361,877 y (ci. 25o- 164) h Claims.

i This invention relates to television systems of the type employingcathode ray tubes and more picture screens for kinescope tubes. I

In television receiving picture tubes a decrease in detail f isencountered due to the halation caused by the electron beam striking thescreen l of fluorescent material. Halation involves -the spreading oflight beyond its proper boundaries. One of the principal causes ofhalation in a `kinescope screen is `the reflection of the vlight fromthe fluorescent material between the surfaces of the member supportingthe fluorescent material. When .the fluorescent material is coated onthe supporting member, light from the fluorescent material is permittedto enter the supporting member at the inner surface over awide angle andhence be reflected from both surfaces to a `comparatively high degree.

Thisreilection can be reduced considerably by decreasing the opticalcontact between the sup porting member and the screen material. I Ifnooptical contact existed between the screen material and the transparentsupporting member, none of the light which enters the supporting memberon the surface of the supporting member adjacent the fluorescentmaterial can experience total reflection at the opposite surface of thesupporting member.

It is practically impossible to reduce the optical contact between thesupporting ymember and screen material sutllciently without experiencingthe trouble from the screen material dropping on? the supporting member.

According to this invention, the optical contact between the screenmaterial and the supporting member can be effectively reduced withoutdecreasing the mechanical support of the screen material. A layer ofsmall transparent particles of glass or quartz is interposed between thescreen material and the supporting member. Therefore, the only eifectivecontact between the fluorescent material and the supporting member isthat comparatively small area of contact between the layer of particlesand the supporting member.

The primary object of this invention is to provide a picture screenfor'a kinescope.

Another object of this invention is to provide a means for reducinghalation in kineseopes.

Other and incidental objects of the invention will beapparent to'thoseskilled in the art `from the following specication considered inconnection with the accompanying drawing, in which Figure 1 is asectional view of a kinescope.

vvention, and

Figure 2 isl a greatly enlarged cross section of a screen in accordancewith one Hform of this inkFigure 3 is anenlarged cross section ofanother v form of this invention.

Referring inmore detail to Fig. l, there is an envelope I containing anelectron gun with an indirectly 4heatedv cathode :3,1 a control.electrode 5, av first anode l, and asecondanode 9. The electron gun isadapted to produce an electron Vbeam which is deflected by thehorizontal vdefiecting coils II aridy the' vertical deilecting coils I3across the image screen I5, the detailv of which is shownmore fully in'Figs. 2 and 3.

Fig. 2 shows a supporting member I 'I which may be the end of theenvelope I of Fig. 1 or it may be a supporting member positioned insidethe envelope I'of Fig. `l upon which there vis a layer of smalltransparent particle'sj I 9 which may be of small polished spheroidalglass or quartz beads. The spheroidalfparticles may be, made adherent tothe supporting member I'I by the use of a suitable binder orby actuallybringing about a' slight sintering action at the points of contactbetween the particles I 9 andthe supporting member I1 under theinilu'ence of heat.

It will be 'noticed that only asmall fraction of the supporting memberI1 is in actual physical contact with the spheroidal particles i9. Theparticles are brought into as close physicalvconvtact with each other asis practically possible.

A coating of fluorescent material 2i is then spread over the surface 'ofthe p/articles.

@In operation, light from the screen material 2| enters the spheroidalparticles from the back side. Due to the close physical or opticalcontact between the fluorescent material 2l and the particles Il, lighttravels in all directions within the particles I! and is eithertransmitted through the particles Il after suifering refraction, or isrei'lected until either scattered at the surface of contact between thefluorescent material 2i and the spheroidal particles I9 or transmittedinto the supporting member at the point of contact between it and thespheroidal particles I9.

The light which is transmitted through the spheroidal particles I9 in anupward direction will enter the supporting member I'I and will betransmitted without experiencing total reflection, because of therelatively small angle from perpendicular that the light intersects thesurtween the spheroidal particles I9 and that light which intersects thesupporting member I'I at angles greater than the critical angle. Sincethe area of the point of contact between the particles I9 and thesupporting member I'l is only a small fraction of the total surface ofthe supporting member II, a marked diminution of the amount of lightsuffering total reflection in the supporting member I'I is broughtabout.

Halation will be further reduced by reason of the fact that light whichexperiences total reflection at the outer surface of the supportingmember II would normally suer total reflection again at the lowersurface unless it impinges upon a region of optical contact with someother particle or object. In the conventional structure, the opticalpoints of contact between the iluorescent material particles and thebulb serve as points for diiiused reflection of the totally reiiectedrays. It is the upwardly directed portion of the diffused reflected rayswhich result in halation with its consequent reduction of detail andcontrast.

Since, in accordance with this invention, only a small fraction of thesupporting member I1 is in contact with the spheroidal particles I9,most of the light totally reected from the upper surface of thesupporting member I1 will be totally reilected again from the lowersurface. This process of reflection will repeat itself with ultimateabsorption of the totally reilected rays.

Fig. 3 shows another form of this invention in which the supportingmember 23 has thereon a layer of irregularly shaped particles 25 whoseoptical contact with the supporting member 23 covers a very smallrelative part of the lower surface of the supporting member 23. Thelayer of fluorescent material 21 covers the lower surface of the mosaicparticles 25. The operation of this form of the invention is similar tothat given above for the form of the invention shown in Fig. 2. Thelight caused by the impinging of the electron beam upon the iluorescentmaterial 21 is caused to reect in the particles 25 until it is projectedinto the supporting member 23 through its point of contact with theparticles 25.

While several systems for carrying this invention into effect have beenindicated in this drawing, it will be apparent to one skilled in the artthat this invention is by no means limited to the particularorganization shown and described but that many modifications may be madewithout departing from the scope of this invention as set forth in theappended claims.

I claim as my invention:

1. In a picture-reproducing system including an envelope and meanspositioned in said envelope for producing an electron beam, a mosaicpositioned in the path of said electron beam and comprising spheroidaltransparent particles having a coating of fluorescent material on thesurface adjacent said electron gun.

2. In a picture-reproducing system including an envelope and meanspositioned in said envel lope for producing an electron beam, an imagescreen positioned in the path of said electron beam and comprising amosaic of transparent particles having a coating thereon of fluorescentmaterial, a transparent member mounted in one end of said envelope uponwhich said particles are supported with substantiallly none of saidfluorescent material in contact therewith.

3. In a picture-reproducing system including an envelope and meanspositioned in said envelope for producing an electron beam, an imagescreen positioned in the path of said electron beam and comprising amosaic of spheroidal transparent particles on one end of said envelopeand said particles having a coating thereon of iluorescent material.

4. In a picture-reproducing system including an envelope and meanspositioned in said envelope for producing an electron beam, an imagescreen positioned in the path of said electron beam and comprising amosaic of transparent particles having a coating thereon of fluorescentmaterial, a transparent member mounted in one end of said envelope uponwhich said particles are adapted to be supported, the total of the areaof contact between the particles and said member being substantiallyless than the area of said mosaic. 5. In a picture-reproducing systemincluding an envelope and means positioned in said envelope forproducing an electron beam, an image screen positioned in the path ofsaid electron beam and comprising a mosaic of spheroidal transparentparticles on one end of said envelope and said particles having acoating thereon of fluorescent material, the total of the area ofcontact between the particles and envelope being substantially less thanthe area of said mosaic.

LOUIS MALTER..Y

